The present invention relates to the field of phototypesetters.
Most phototypesetters produced over the past decades employ rotatable font carriers which bear images of characters to be phototypeset. A flash lamp, under the control of digital address circuitry, sequentially flashes selected character images upon the font carrier, to produce light images which are projected through an optical system to be focused upon a photosensitive material, such optical systems also employing means for changing the character image sizes. In the phototypesetting industry, such optical character size changing devices have employed relatively large quantities of moving parts, have been costly, and have been somewhat unreliable. While optical zoom systems have been employed, relatively tedious manual adjustments of the position of the lenses with respect to their mounting devices have been required during manufacture to compensate for lens parameter variations with respect to the theoretically correct or target values. For example, variations in focal length have been compensated for, to maintain accurate focus, by mounting the lenses in a threaded sleeve which is rotated by the operator to produce fine changes in the lens position along the optical axis. Furthermore, lenses have been mounted in oversized apertures and their positions in the x and y directions lying in a plane perpendicular to the optical axis (z axis) have been adjusted by tapping in order to translate the lenses in the plane perpendicular to the optical axis, to reduce base line errors (vertical positioning) and side of character errors (horizontal positioning). It is thus desirable to eliminate these tedious manual manipulations upon manufacture of the phototypesetters.
It is also desirable to employ a single stepping motor for actuating the scanning or escapement carriage and at the same time to employ this motor to actuate the lens carriages which must be moved along the optical axis with changes in character size, and additionally to employ this same motor to actuate a font disc track select carriage.
It is furthermore desirable to provide a simple and reliable driving system for positioning these carriages with great accuracy and reliability and yet be inexpensive to manufacture. Furthermore, it is desirable to reduce manufacturing costs by mounting lenses into the phototypesetter having loose manufacturing tolerances, and which individual tolerance variations may be compensated for in the easy and rapid generation of digital positioning command codes which are customized for each particular machine during manufacture to eliminate the effect of such variations.